The invention relates generally to the field of multi-carrier CDMA systems and more particularly, to systems and methods of channel coding and inverse-multiplexing in a multi-channel CDMA system to obtain higher data rates using lower rate channels.
In multi-carrier CDMA systems, as discussed in TR45.5 and CDMA Development Group (CDG) one option for third generation CDMA systems is for user data to be simultaneously carried on multiple carriers. In the third generation of Personal Communication Systems (PCS), an information data rate of as much as 2 Mbps for indoor, and fixed wireless systems, as required by ITU, is to be supported over a system bandwidth of 5 MHz and above. The current CDMA systems defined in the IS-95 standard of the Telecommunications Industry Association and the Electronic Industries Association (TIA/EIA/IS-95), supports a maximum information rate of 14.4 kbps on a 1.25 MHZ bandwidth.
Currently, there are two basic approaches being considered for utilizing the wider bandwidth in a third generation CDMA system. First, is the Direct Spread approach where signals are spread onto the entire bandwidth using one carrier. This approach suffers from the problem of not being compatible with the present CDMA systems (i.e. it is not backwards compatible). The second approach is a multi-carrier approach.
Dividing the bandwidth into N sub-bands and simultaneously spreading identical symbols onto each of the sub-bands has been proposed by Lucent Technologies, for example. While this approach overcomes the problem associated with the first approach (Direct Spread which is not backwards compatible) it suffers from the problem of underutilizing the data rate capability of the system.
Accordingly there exists a need for a system and method of utilizing the wider multi-carrier bandwidth that is backwards compatible and efficiently utilizes the enhanced data rate capabilities of the wider bandwidth.
A need also exists for such a system which accurately communicates information from the transmitter to the receiver.
Further, a need exists for a system which uses multiple slower data streams to carry the same amount of data as a single faster data stream.
A need also exists for a CDMA system that can coexist in the same frequency spectrum, or overlay, existing CDMA carriers so that available bandwidth and channel capacity can be dynamically shared between existing systems and new systems.
Accordingly it is an object of the present invention to provide systems and methods of communicating over a wider bandwidth in a manner which is compatible with present CDMA systems.
It is another object of the present invention to provide such a system and method which efficiently utilizes the communication capabilities of a wider bandwidth.
It is a further object of the present invention to provide such systems and methods which accurately communicate information from a transmitter to a receiver.
It is yet another object of the present invention to provide systems and methods of communicating information from a transmitter to a receiver which may utilize multiple slower data streams yet still provide the same aggregate rate of transmission as a single faster data stream.
Another object of the present invention is to provide a CDMA system that can coexist in the same frequency spectrum, or overlay, existing CDMA carriers so that available bandwidth and channel capacity can be dynamically shared between existing systems and new systems.
These and other objects of the invention will become apparent to those skilled in the art from the following description thereof.
In accordance with the teachings of the present invention, these and other objects may be accomplished by the present systems and methods of channel coding and inverse-multiplexing for multi-carrier CDMA systems. The present invention includes a data stream which may be encoded with error correction, interleaved, inverse-multiplexed onto a plurality of communication channels such that one portion of the data stream is spread onto a first communication channel and another portion of the data stream is spread onto a second communication channel.
In an exemplary embodiment of the invention, the system includes an error correction encoder configured to add error correction bits to a data stream. It also includes an interleaver and a inverse-multiplexor configured to spread the data stream over multiple communication channels. These components may be arranged in various configurations.
In another embodiment of the invention, the system includes encoding means for encoding a data stream with error correction bits, interleaver means for interleaving the data stream, multiplexing means for multiplexing at least one power control symbol onto the data stream, and inverse-multiplexor means for inverse-multiplexing the data stream onto a plurality of communication channels. These components may also be arranged in different configurations.
The invention will next be described in connection with certain exemplary embodiments; however, it should be clear to those skilled in the art that various modifications, additions and subtractions can be made without departing from the spirit or scope of the claims.